The invention relates broadly to fillers containing inorganic oxide particles for use in dental materials. Specifically, the fillers of the invention are clusters comprising a plurality of at least two amorphous, inorganic oxides: non-heavy metal oxide particles and a heavy metal oxide. The fillers mixed in a hardenable resin provide radiopaque dental materials that have high strength, good aesthetic character, and good retention of polish.
Dental materials generally have unique requirements as compared to the broad spectrum of composite materials. For health reasons, dental materials should be suitable for use in the oral environment. In certain instances, durability of a dental material is important to ensure satisfactory performance. For example, dental work that is performed at dentition locations where mastication forces are generally great, high strength and durability is desirable. In other instances, aesthetic character or quality is highly desired. This is often the case where dental work is performed at locations where a tooth repair or restoration can be seen from a relatively short distance.
Strength of a dental material is typically a result of the addition of fillers. Generally, to provide a dental material possessing greater mechanical strength characteristics, a material is filled or loaded with larger sized particles; i.e. particles that are generally greater than about 0.4 micrometers in diameter. These materials are often referred to as hybrid composites. A disadvantage to these composites, however, is their tendency to lack luster and aesthetic character, especially after exposure to repetitive tooth brushing, a requirement for good oral hygiene.
It is generally desired that the dental restorative material blend well with the surrounding dentition and looks life-like. Aesthetic quality in dental materials is typically achieved by creating material that has tooth-like colors/shades. xe2x80x9cMicrofills,xe2x80x9d a certain class of dental materials, tend to have some luster, to better replicate tooth appearance. One example of a xe2x80x9cmicrofillxe2x80x9d is commercially available under the trade designation SILUX PLUS (3M Co., St. Paul, Minn.). Microfills, however, generally have less mechanical strength than hybrid composites or xe2x80x9cmacrofills.xe2x80x9d
Radiopacity of a dental material can be useful in dentistry. Radiopaque composites can be examined using standard dental X-ray equipment, thereby facilitating long term detection of marginal leakage or caries in tooth tissues adjacent to a cured composite. U.S. Pat. No. 4,503,169 describes a radiopaque, low visual opacity (i.e. translucent) dental composite with non-vitreous zirconia-silica microparticles made by a sol-gel process. The process involves a sintering step followed by milling of the fired filler.
The invention provides fillers useful in dental materials to provide strong, highly aesthetic, radiopaque materials. Advantageously, the fillers in a hardenable resin provide dental materials that able to retain their polish after repetitive abrasive contact. The filler comprises a substantially amorphous cluster of non-heavy metal oxide particles and a heavy metal oxide, where the cluster has an average diameter of less than about 5 xcexcm. More preferably the cluster has an average diameter of less than 2 xcexcm.
xe2x80x9cHardenablexe2x80x9d is descriptive of a material that can be cured or solidified e.g., by heating to remove solvent, heating to cause polymerization, chemical crosslinking, radiation-induced polymerization or crosslinking, or the like.
xe2x80x9cNon-heavy metal oxidexe2x80x9d means any oxide of elements other than those of heavy metals.
xe2x80x9cHeavy metal oxidexe2x80x9d means an oxide of metals having an atomic number greater than 28.
In one aspect of the invention, the non-heavy metal oxide particles are silica particles.
In another aspect of the invention, the heavy metal oxide is zirconium oxide.
In yet another aspect of the invention, the filler can be loaded into a hardenable resin to provide dental materials having radiopacity, low visual opacity, high mechanical strength and high aesthetic character.
In a further aspect of the invention, the fillers of the invention can be used in dental materials such as adhesives, artificial crowns, anterior or posterior fillings, casting materials, cavity liners, cements, coating compositions, mill blanks, orthodontic devices, restoratives, prostheses, and sealants.